Mass spectrometry is an analytical method of identifying and characterizing compositions and structures by separating and detecting compounds according to their different mass to charge ratios (m/z). Because of its high specificity and sensitivity, mass spectrometry has an increasingly important role in the field of biological analysis. Bio-mass spectrometry (Bio-MS) is a mass spectrometry technique in the analysis of biomolecules and has been widely used in protein and peptide research, such as protein relative molecular mass determination, peptide mass fingerprinting, peptide sequencing technology, mercapto and disulfide bond localization, protein post-translational modification, quantitative proteome analysis, protein interaction studies, etc. In addition, the bio-mass spectrometry has also been used in structural determination of polysaccharides, oligonucleotides and nucleic acid analysis, microbial identification, drug research and development, and other fields.
The ion source of a mass spectrometer is one of the components that greatly affect the detection sensitivity of the spectrometer. For the detection of a liquid sample, the most common ion source is (nanoliter) electrospray ionization source. The electrospray ionization source uses an electric field to produce charged droplets, which undergo a desolvation process and become analyte ions for mass spectrometry analysis. This process includes three stages: formation of charged droplets, droplets shrinkage, and gas phase ions formation. More recently, nanoliter electrospray ionization source was developed, which greatly reduced the amount of samples required and the flow rate. Electrospray ionization source is widely used in LC-MS interface.
On the other hand, when using electrospray ionization source to detect multi-component samples, ionization competition may occur between the components to be detected, as well as between the to-be-detected components and impurities. Therefore, components with a low abundance and low ionization efficiency may not be detected easily. As a result, in practice, the samples often need to be pre-treated and pre-separated before use. In order to simplify the pretreatment process for complex samples and eliminate the influence of the pretreatment process on the components in this process, the present invention provides improved design over the conventional electrospray method and uses electric field to separate the samples in the ionization process based on their charge property, thereby reducing competition between the components of the sample and improving the ionization efficiency of individual components, and in particular, achieving multi-mode separation in the combination process.